The invention relates to soldering of plate-shaped circuit carriers inside an inert gas wave soldering means wherein the reaction chamber is gas-sealed from the environment and contains at least one wave solder bath and at least one jet for the introduction of heated inert gas.
Flux-free or inert gas soldering is a known technique in the construction of thick film circuits and has proven advantageous over conventional soldering with flux in an air atmosphere. A number of soldering defects, such as, for example, solder bridges, solder pegs and bubbles, which are exclusively or at least in part due to the influence of the flux employed can be avoided by such soldering in inert gas.
A flow bath solder means encapsulated on all sides to form a reaction chamber is gas-sealed from the ambient environment in the known inert gas soldering operation. By means of supplying an oxygen-free inert gas, a forming gas such as nitrogen, an atmosphere is produced in the reaction chamber, in which the soldering process can be executed without the influence of a fluxing agent. It is necessary or at least expedient to heat the circuit carrier before or during its transport to the solder flow bath. Typically, the solder flow bath is disposed in the central region of an encapsulated or chamber channel that has a suitable planar cross-section matched to the dimensions of the circuit carriers to be soldered. Heating elements to heat the circuit carriers are disposed in the channel in the area in front of the solder flow bath. The inert gas is blown into the channel through a plurality of jets preceding as well as following the solder flow bath. The inert gas creates a slight overpressure inside the channel such that it flows out in turn at the channel entrance and exit, whereby penetration of ambient air into the inside of the channel is prevented.
Attempts to apply the known inert gas soldering method to soldering conventional printed circuit boards, wherein the connector posts are disposed on one face and the circuit components are disposed on the other opposed face of the printed circuit board have heretofore been unsuccessful. The present invention, however, concerns a way that inert gas soldering can also be employed for conventional printed circuit boards.